U.S. patent application number 15/543409 was filed with the patent office on 2017-12-21 for surface treated steel sheet for fuel tank.
This patent application is currently assigned to NIPPON STEEL & SUMITOMO METAL CORPORATION. The applicant listed for this patent is NIPPON STEEL & SUMITOMO METAL CORPORATION. Invention is credited to Kiyokazu ISHIZUKA, Ikuo KIKUCHI, Noriyuki MAEKAWA, Kenichiro MATSUMURA, Hidetoshi SHINDO, Hiroaki URAMOTO.
Application Number | 20170362732 15/543409 |
Document ID | / |
Family ID | 56417136 |
Filed Date | 2017-12-21 |
United States Patent
Application |
20170362732 |
Kind Code |
A1 |
ISHIZUKA; Kiyokazu ; et
al. |
December 21, 2017 |
SURFACE TREATED STEEL SHEET FOR FUEL TANK
Abstract
Provided is a surface treated steel sheet for a fuel tank, the
surface treated steel sheet including: a Zn plated layer or a
Zn--Ni alloy plated layer which is formed on at least a surface of
the steel sheet to be an inner surface of the fuel tank; and a
chromate-free chemical conversion coating layer containing a
water-and-oil repellent, the chromate-free chemical conversion
coating layer being placed over the Zn plated layer or the Zn--Ni
alloy plated layer on the surface to be the inner surface of the
fuel tank. A water contact angle on a surface of the chromate-free
chemical conversion coating layer is more than or equal to 70
degrees and an n-hexadecane contact angle on the surface of the
chromate-free chemical conversion coating layer is more than or
equal to 30 degrees and less than or equal to 70 degrees.
Inventors: |
ISHIZUKA; Kiyokazu; (Tokyo,
JP) ; MAEKAWA; Noriyuki; (Tokyo, JP) ;
URAMOTO; Hiroaki; (Tokyo, JP) ; SHINDO;
Hidetoshi; (Tokyo, JP) ; KIKUCHI; Ikuo;
(Tokyo, JP) ; MATSUMURA; Kenichiro; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NIPPON STEEL & SUMITOMO METAL CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
NIPPON STEEL & SUMITOMO METAL
CORPORATION
Tokyo
JP
|
Family ID: |
56417136 |
Appl. No.: |
15/543409 |
Filed: |
January 20, 2016 |
PCT Filed: |
January 20, 2016 |
PCT NO: |
PCT/JP2016/051559 |
371 Date: |
July 13, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B32B 1/02 20130101; B60K
2015/03032 20130101; B62J 35/00 20130101; C23C 28/3225 20130101;
B60K 15/03 20130101; C23C 22/42 20130101; C23C 28/34 20130101; C23C
2/06 20130101; C23C 22/08 20130101; C25D 3/22 20130101; C25D 7/00
20130101; C23C 22/06 20130101; C25D 3/56 20130101; C23C 22/44
20130101; C23C 2222/20 20130101; C23C 2/26 20130101; B65D 85/84
20130101; C23C 2/40 20130101; C25D 5/48 20130101; B32B 15/18
20130101 |
International
Class: |
C25D 7/00 20060101
C25D007/00; C25D 3/22 20060101 C25D003/22; B65D 85/84 20060101
B65D085/84; C25D 3/56 20060101 C25D003/56; C23C 22/06 20060101
C23C022/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 21, 2015 |
JP |
2015-009535 |
Claims
1. A surface treated steel sheet for a fuel tank, the surface
treated steel sheet comprising: a Zn plated layer or a Zn--Ni alloy
plated layer which is placed on a surface to be an inner surface of
the fuel tank, the surface being a base metal, or on the surface to
be the inner surface of the fuel tank and a surface to be an outer
surface of the fuel tank, the surface being the base metal; and a
chromate-free chemical conversion coating layer containing a
water-and-oil repellent, the chromate-free chemical conversion
coating layer being placed over the Zn plated layer or the Zn--Ni
alloy plated layer, wherein a water contact angle on a surface of
the chromate-free chemical conversion coating layer is more than or
equal to 70 degrees and an n-hexadecane contact angle on the
surface of the chromate-free chemical conversion coating layer is
more than or equal to 30 degrees and less than or equal to 70
degrees.
2. The surface treated steel sheet for a fuel tank according to
claim 1, wherein only the surface to be the inner surface of the
fuel tank, the surface being the base metal, is provided with the
chromate-free chemical conversion coating layer and one of the Zn
plated layer and the Zn--Ni alloy plated layer, and the surface to
be the outer surface of the fuel tank, the surface being the base
metal, is not provided with the chromate-free chemical conversion
coating layer and the one of the Zn plated layer and the Zn--Ni
alloy plated layer.
3. The surface treated steel sheet for a fuel tank according to
claim 2, wherein a deposition amount of Zn and/or Ni on the surface
to be the outer surface of the fuel tank, the surface being the
base metal, is 0.01 to 0.5 g/m.sup.2.
4. The surface treated steel sheet for a fuel tank according to
claim 1, wherein a deposition amount of the Zn plated layer or the
Zn--Ni alloy plated layer is 5 to 40 g/m.sup.2 per surface.
5. The surface treated steel sheet for a fuel tank according to
claim 1, wherein a Ni content in the Zn--Ni alloy plated layer is 9
to 14 mass % with respect to a total mass of the Zn--Ni alloy
plated layer.
6. The surface treated steel sheet for a fuel tank according to
claim 1, wherein a deposition amount of the chromate-free chemical
conversion coating layer is 0.1 to 2 g/m.sup.2.
7. The surface treated steel sheet for a fuel tank according to
claim 1, wherein the chromate-free chemical conversion coating
layer contains, as the water-and-oil repellent, a fluorine-based
water-and-oil repellent.
8. The surface treated steel sheet for a fuel tank according to any
one of claims 1 to 7, wherein the chromate-free chemical conversion
coating layer further contains a polyolefin lubricant.
9. The surface treated steel sheet for a fuel tank according to
claim 1, wherein the chromate-free chemical conversion coating
layer is an inorganic coating film, and does not contain an organic
resin component other than the water-and-oil repellent.
10. The surface treated steel sheet for a fuel tank according to
claim 8, wherein the chromate-free chemical conversion coating
layer is an inorganic coating film, and does not contain an organic
resin component other than the water-and-oil repellent and the
polyolefin lubricant.
Description
TECHNICAL FIELD
[0001] The present invention relates to a surface treated steel
sheet for a fuel tank.
BACKGROUND ART
[0002] With tightening environmental regulation in recent years,
market needs for materials that do not contain harmful metals have
been increased. For example, in the field of automobiles, the
switching from a lead-tin alloy plated steel sheet, which has been
a main ingredient of fuel tanks, to a material not containing lead
has been promoted. Here, to a unique required performance of the
fuel tanks, which is high inner corrosion resistance under the
environment in which a fuel is enclosed (hereinafter, referred to
as fuel corrosion resistance), many suggestions are given involving
using zinc-based plated steel sheets, which achieve steady success
as inner and outer sheets of automobiles (for example, see the
following Patent Literatures 1 to 3).
CITATION LIST
TABLE-US-00001 [0003] Patent Literature Patent Literature 1: JP
H5-106058A Patent Literature 2: JP H9-324279A Patent Literature 3:
JP 2004-169122A Patent Literature 4: JP 2007-186745A Patent
Literature 5: WO 2010/061964 Patent Literature 6: WO
2008/059890
SUMMARY OF INVENTION
Technical Problem
[0004] However, the technologies according to Patent Literatures 1
to 3 each have an assumption that chromate treatment is performed,
and therefore are incompatible with the recent market needs for
materials that do not contain harmful metals. For this reason, a
chromate-free zinc-based plated steel sheet for a fuel tank is
disclosed (for example, see Patent Literatures 4 to 6). Compared to
the conventional zinc-based plated steel sheet subjected to the
chromate treatment, the chromate-free zinc-based plated steel sheet
is not sufficient in fuel corrosion resistance under a severer
environment (for example, corrosion resistance over a longer time
period, and corrosion resistance in the case where damage in the
coating film has occurred during processing), and requires
improvement.
[0005] Patent Literature 4 discloses a chromate-free coating film
mainly containing an organic resin. However, when such a
chromate-free coating film mainly containing an organic resin is
exposed to a fuel environment for a long time period, the organic
resin is swelled by the fuel, and adhesion between surfaces of
plating decreases. It is assumed that such swelling of the organic
resin is a factor in insufficient corrosion resistance.
[0006] Patent Literature 5 discloses a galvanized steel sheet
having a coating film formed by applying an aqueous treatment agent
containing an organosilicon compound and an organofluorine compound
to a zinc-based plated steel sheet and drying or baking the
resultant. Further, Patent Literature 6 discloses a galvanized
steel sheet having a composite coating film containing an
organosilicon compound, a fluorocompound, a vanadium compound, and
a lubricant. However, those steel sheets are improved in corrosion
resistance, but are not imparted with corrosion resistance with
respect to deteriorated gasoline.
[0007] Accordingly, the present invention aims to provide a surface
treated steel sheet for a fuel tank, which exhibits excellent
corrosion resistance under an environment in which various fuels
are enclosed, the fuels including a fuel containing an organic acid
such as deteriorated gasoline and a fuel containing dew
condensation water in addition to an organic acid, and which has
satisfactory press workability. The present invention also aims to
obtain the above characteristics without using lead and chromate
treatment.
Solution to Problem
[0008] The inventors of the present invention have investigated the
improvement in fuel corrosion resistance in a chromate-free
zinc-based plated steel sheet, and have found that the fuel
corrosion resistance can be remarkably improved by making a
zinc-based plated layer to be a Zn plated layer or a Zn--Ni alloy
plated layer, and imparting not only water repellency but also oil
repellency to a surface of the plated layer. Further, the inventors
of the present invention have found that, on the contrary, in the
case where the oil repellency is excessively imparted, the fuel
corrosion resistance decreases and the press workability also
remarkably decreases. As a result of carrying out investigation on
the basis of those findings, the inventors of the present invention
have found that a steel sheet which is excellent in fuel corrosion
resistance and press workability can be obtained by forming a
coating film having predetermined water repellency and oil
repellency on a surface to be an inner surface of a fuel tank. That
is, the gist of the present invention is as follows. [0009] (1)
[0010] A surface treated steel sheet for a fuel tank, the surface
treated steel sheet including:
[0011] a Zn plated layer or a Zn--Ni alloy plated layer which is
placed on a surface to be an inner surface of the fuel tank, the
surface being a base metal, or on the surface to be the inner
surface of the fuel tank and a surface to be an outer surface of
the fuel tank, the surface being the base metal; and
[0012] a chromate-free chemical conversion coating layer containing
a water-and-oil repellent, the chromate-free chemical conversion
coating layer being placed over the Zn plated layer or the Zn--Ni
alloy plated layer,
[0013] wherein a water contact angle on a surface of the
chromate-free chemical conversion coating layer is more than or
equal to 70 degrees and an n-hexadecane contact angle on the
surface of the chromate-free chemical conversion coating layer is
more than or equal to 30 degrees and less than or equal to 70
degrees. [0014] (2)
[0015] The surface treated steel sheet for a fuel tank according to
(1), wherein
[0016] only the surface to be the inner surface of the fuel tank,
the surface being the cold-rolled steel sheet, is provided with the
chromate-free chemical conversion coating layer and one of the Zn
plated layer and the Zn--Ni alloy plated layer, and
[0017] the surface to be the outer surface of the fuel tank, the
surface being the cold-rolled steel sheet, is not provided with the
chromate-free chemical conversion coating layer and the one of the
Zn plated layer and the Zn--Ni alloy plated layer. [0018] (3)
[0019] The surface treated steel sheet for a fuel tank according to
(2), wherein a deposition amount of Zn and/or Ni on one surface of
the fuel tank, the surface being the cold-rolled steel sheet, is
0.01 to 0.5 g/m.sup.2. [0020] (4)
[0021] The surface treated steel sheet for a fuel tank according to
any one of (1) to (3), wherein
[0022] a deposition amount of the Zn plated layer or the Zn--Ni
alloy plated layer is 5 to 40 g/m.sup.2 per surface. [0023] (5)
[0024] The surface treated steel sheet for a fuel tank according to
any one of (1) to (4), wherein
[0025] a Ni content in the Zn--Ni alloy plated layer is 9 to 14
mass % with respect to a total mass of the Zn--Ni alloy plated
layer. [0026] (6)
[0027] The surface treated steel sheet for a fuel tank according to
any one of (1) to (5), wherein
[0028] a deposition amount of the chromate-free chemical conversion
coating layer is 0.1 to 2 g/m.sup.2. [0029] (7)
[0030] The surface treated steel sheet for a fuel tank according to
any one of (1) to (6), wherein
[0031] the chromate-free chemical conversion coating layer
contains, as the water-and-oil repellent, a fluorine-based
water-and-oil repellent. [0032] (8)
[0033] The surface treated steel sheet for a fuel tank according to
any one of (1) to (7), wherein
[0034] the chromate-free chemical conversion coating layer further
contains a polyolefin lubricant. [0035] (9)
[0036] The surface treated steel sheet for a fuel tank according to
any one of (1) to (7), wherein
[0037] the chromate-free chemical conversion coating layer is an
inorganic coating film, and does not contain an organic resin
component other than the water-and-oil repellent. [0038] (10)
[0039] The surface treated steel sheet for a fuel tank according to
(8), wherein
[0040] the chromate-free chemical conversion coating layer is an
inorganic coating film, and does not contain an organic resin
component other than the water-and-oil repellent and the polyolefin
lubricant.
Advantageous Effects of Invention
[0041] According to the present invention, there can be provided a
surface treated steel sheet for a fuel tank, which exhibits
excellent corrosion resistance under an environment in which
various fuels are enclosed, the fuels including a fuel containing
an organic acid such as deteriorated gasoline and a fuel further
containing dew condensation water in addition to an organic acid,
and which has satisfactory press workability.
DESCRIPTION OF EMBODIMENTS
[0042] The present invention relates to a zinc-based steel sheet
for a fuel tank, which is excellent in corrosion resistance to
various fuels and press workability, is not subjected to lead and
chromate treatment, and is environmentally friendly. The present
invention also relates to a steel sheet used for an automobile, a
motorcycle, industrial machinery, and construction machinery, and
in addition, used for a tank in which a fuel is enclosed and a part
of the tank.
[0043] The steel sheet for a fuel tank according to the present
invention includes: a Zn plated layer or a Zn--Ni alloy plated
layer (hereinafter, also referred to as plated layer) which is
placed on a surface to be an inner surface of the fuel tank, the
surface being a base metal (one surface), or on the surface to be
the inner surface of the fuel tank and a surface to be an outer
surface of the fuel tank (both surfaces); and a chromate-free
chemical conversion coating layer (hereinafter, also referred to as
chemical conversion coating layer) containing a water-and-oil
repellent, the chemical conversion coating layer being placed over
the Zn plated layer or the Zn--Ni alloy plated layer. Further, a
water contact angle on a surface of the chemical conversion coating
layer is more than or equal to 70 degrees, and an n-hexadecane
contact angle on the surface of the chemical conversion coating
layer is more than or equal to 30 degrees and less than or equal to
70 degrees.
[0044] In the steel sheet of the present invention, the surface to
be the outer surface of the fuel tank (hereinafter, referred to as
outer surface) may have the Zn plated layer or the Zn--Ni alloy
plated layer, or does not necessarily have the Zn plated layer or
the Zn--Ni alloy plated layer. However, in order to make the
weldability of the steel sheet satisfactory, it is preferred that
the surface to be the outer surface of the fuel tank do not have
the plated layer. Further, for example, in the case where the steel
sheet is used as a fuel tank for a motorcycle which places
importance on the visual quality of the coating of the outer
surface of the fuel tank, it is preferred that the outer surface of
the fuel tank do not have the plated layer in order to make the
external appearance of the coating satisfactory. On the other hand,
in the case where the steel sheet is used for the case where the
outer surface of the fuel tank also requires high corrosion
resistance, it is preferred that the outer surface of the fuel tank
have the plated layer. In the steel sheet according to the present
invention, the presence and absence of the plated layer on the
outer surface and the inner surface can be controlled in accordance
with the use. Note that the chromate-free chemical conversion
coating layer is not formed over: the Zn plated layer or the Zn--Ni
alloy plated layer on the surface to be the outer surface of the
fuel tank; or the steel sheet surface which does not have the Zn
plated layer or the Zn--Ni alloy plated layer. The water contact
angle and the n-hexadecane contact angle can be measured by a known
measurement method using a contact angle meter.
[0045] It is necessary that the water contact angle and the
n-hexadecane contact angle on the surface of the chromate-free
chemical conversion coating layer at the surface to be the inner
surface of the fuel tank be more than or equal to 70 degrees, and
more than or equal to 30 degrees and less than or equal to 70
degrees, respectively. In the case where the water contact angle is
less than 70 degrees, the corrosion resistance with respect to
deteriorated gasoline is insufficient. It is preferably more than
or equal to 80 degrees. The upper limit of the water contact angle
is not particularly defined (which does not exceed 180 degrees
theoretically), but the level of the upper limit that can be
achieved on the chromate-free chemical conversion coating layer
placed over an ordinary Zn plated layer or Zn--Ni alloy plated
layer is around 120 degrees. In the case where the water contact
angle is large, it is assumed that the corrosion resistance
improves, since isolation effects are large owing to dew
condensation water in which corrosion factors such as organic
matters in the deteriorated gasoline are concentrated. In order to
obtain sufficient corrosion resistance with respect to deteriorated
gasoline, it is not sufficient only to define the water contact
angle to the above range, and it is also necessary to control an
oil contact angle.
[0046] Further, in the present invention, the n-hexadecane contact
angle on the surface of the chromate-free chemical conversion
coating layer at the surface to be the inner surface of the fuel
tank is more than or equal to 30 degrees and less than or equal to
70 degrees. The n-hexadecane contact angle on the surface of the
chromate-free chemical conversion coating layer is more preferably
more than or equal to 55 degrees and less than or equal to 70
degrees. Here, n-hexadecane is used as an imitation component of
fuel oil. In the case where the n-hexadecane contact angle on the
surface of the chemical conversion coating layer is less than 30
degrees, corrosion resistance with respect to deteriorated gasoline
is insufficient. The reason therefor is not necessarily clear, but
it can be considered that, in the case where the contact angle is
small, the deteriorated gasoline erodes the coating film from a
point at which a flaw caused by press working or the like occurs.
Further, in the case where the n-hexadecane contact angle on the
surface of the chemical conversion coating layer exceeds 70
degrees, primary rust resistance of the opposite surface of the
steel sheet (the surface to be the outer surface of the fuel tank)
remarkably decreases. The reason therefor is that the steel sheet
for a fuel tank is generally shipped after: the plated layer and
the chemical conversion coating layer are formed in a production
line; then rust-resistant oil for the primary rust resistance is
applied; and the resultant is wound in a coil shape. To be
specific, in the case where the steel sheet is wound in a coil
shape, the surface to be the outer surface of the fuel tank (that
is, the Zn plated surface or the Zn--Ni alloy plated surface which
does not have the chemical conversion coating layer, or the
non-plated surface) faces the surface to be the inner surface of
the fuel tank (that is, the surface of the chromate-free chemical
conversion coating layer having water repellency and oil
repellency). Here, in the case where the n-hexadecane contact angle
on the surface to be the inner surface of the fuel tank exceeds 70
degrees, the surface of the chemical conversion coating layer
excessively repels the rust-resistant oil. Since such an effect
influences the surface to be the outer surface of the fuel tank
that faces the surface to be the inner surface of the fuel tank in
the state of being stacked in the coil shape, under the
high-temperature and high-humidity condition, rust occurs from the
part that lacks the rust-resistant oil on the surface that faces
the surface to be the inner surface of the fuel tank (that is, on
the surface to be the outer surface of the fuel tank). This
phenomenon is fatal particularly in the case where the surface to
be the outer surface of the fuel tank is a non-plated surface.
[0047] In addition, the above-mentioned steel sheet having poor
primary rust resistance also has a poor coating property in the
case where a fuel tank is produced after the steel sheet is kept in
the coiled state for a long period of time. In the fuel tank
produced using the steel sheet, the inner surface is generally the
steel sheet as it is whose surface has been treated, but the outer
surface is generally coated. Particularly in a tank for a
motorcycle, since the importance is placed on the visual quality of
the coating of the surface to be the outer surface of the fuel
tank, the coating property of the outer surface is an important
characteristic. Here, although no abnormality such as rust that can
be visually recognized is found through a primary rust resistance
test, there is a case where a slight surface layer oxide
film-unevenness may cause coating unevenness. Therefore, the
n-hexadecane contact angle on the surface to be the inner surface
being less than or equal to 70 degrees can suppress the decrease in
the rust resistance and the coating property. In addition, it is
more preferred that the surface to be the outer surface be a
non-plated surface. This is because, in the case where the Zn
plated layer or the Zn--Ni alloy plated layer is provided as the
surface to be the outer surface, although the n-hexadecane contact
angle on the surface to be the inner surface is more than or equal
to 30 degrees, which is within the range of the present invention,
and no rust occurs in the primary rust resistance test, a slight
zinc oxide film-unevenness is likely to occur and the coating
property may decrease.
[0048] Further, in the case where the n-hexadecane contact angle
exceeds 70 degrees, the corrosion resistance with respect to the
deteriorated gasoline may decrease, which is not preferred. This is
because, as will be described later, in the case where the
n-hexadecane contact angle exceeds 70 degrees, oil-repellency
becomes remarkable, so that the press workability lowers, and
damage in the coating film and the plating may become severe.
[0049] On the other hand, in the steel sheet according to the
present invention, since the n-hexadecane contact angle on the
surface to be the inner surface of the fuel tank is more than or
equal to 30 degrees and less than or equal to 70 degrees, the steel
sheet repels oil to a certain extent during the press working, but
it does not pose a problem on practical use of the press working.
Moreover, in the present invention, in the case where the surface
to be the outer surface of the fuel tank is the Zn plated surface
or the Zn--Ni alloy plated surface, or the non-plated surface,
since those surfaces do not repel the oil, the press workability
further improves. In this way, the press workability of the steel
sheet according to the present invention can be further enhanced by
making the surface to be the inner surface of the fuel tank
different from the surface to be the outer surface of the fuel
tank.
[0050] Here, in the steel sheet according to the present invention,
the steel sheet (base metal) used as a base material is not
particularly limited, and any steel sheet is usable as long as it
is a steel sheet that is generally used as a base material of a
zinc-based plated steel sheet.
[0051] The Zn plated layer or the Zn--Ni alloy plated layer formed
on at least one surface of the steel sheet (base metal) according
to the present invention is an alloy plated layer containing at
least zinc or an alloy of zinc and nickel. The Zn plated layer or
the Zn--Ni alloy plated layer can be formed by a known plating
method such as an electroplating method.
[0052] The deposition amount of the Zn plated layer or the Zn--Ni
alloy plated layer in the steel sheet according to the present
invention is preferably 5 to 40 g/m.sup.2 per surface. In the case
where the deposition amount of the Zn plated layer or the Zn--Ni
alloy plated layer per surface is less than 5 g/m.sup.2, it is not
preferred because the corrosion resistance with respect to
deteriorated gasoline is likely to be insufficient. Further, in the
case where the deposition amount of the Zn plated layer or the
Zn--Ni alloy plated layer per surface exceeds 40 g/m.sup.2, it is
not preferred because it is disadvantageous in terms of cost.
[0053] Moreover, the Ni content in the Zn--Ni alloy plated layer is
preferably 9 to 14 mass % with respect to a total mass of the
Zn--Ni alloy plated layer. In the case where the Ni content is in
this range, the corrosion resistance with respect to deteriorated
gasoline in particular becomes satisfactory. Note that the Zn
plated layer or the Zn--Ni alloy plated layer may contain a known
third component (for example, metal such as Fe, Co, Sn, and Cr),
and the underneath the Zn plated layer or the Zn--Ni alloy plated
layer may be subjected to known pre-plating (for example,
pre-plating of Fe and Ni).
[0054] The steel sheet for a fuel tank according to the present
invention includes the chromate-free chemical conversion coating
layer (hereinafter, also referred to as chemical conversion coating
layer) containing a water-and-oil repellent, the chemical
conversion coating layer being placed over the Zn plated layer or
the Zn--Ni alloy plated layer on the surface to be the inner
surface of the fuel tank. The deposition amount of the
chromate-free chemical conversion coating layer in the steel sheet
according to the present invention is preferably 0.1 to 2
g/m.sup.2. In the case where the deposition amount of the
chromate-free chemical conversion coating layer is less than 0.1
g/m.sup.2, it is not preferred because the corrosion resistance
with respect to deteriorated gasoline is likely to be insufficient.
In the case where the deposition amount of the chromate-free
chemical conversion coating layer exceeds 2 g/m.sup.2, it is not
preferred because the workability and weldability may
deteriorate.
[0055] In order to achieve the water contact angle and the
n-hexadecane contact angle on the surface to be the inner surface
of the fuel tank in the steel sheet according to the present
invention, it is necessary that the chromate-free chemical
conversion coating layer contain a water-and-oil repellent. In
particular, it is preferred that the chromate-free chemical
conversion coating layer contain a fluorine-based water-and-oil
repellent. Any fluorine-based resin having a C--F bond may be used
as the fluorine-based water-and-oil repellent, and examples thereof
include polytetrafluoroethylene,
tetrafluoroethylene-hexafluoropropylene copolymer,
tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer,
polychlorotrifluoro ethylene, polyvinylidene fluoride, polyvinyl
fluoride, ethylene-tetrafluoroethylene copolymer,
ethylene-chlorotrifluoroethylene copolymer, and perfluoroalkyl
group-containing polymer. The content of the fluorine-based
water-and-oil repellent in the chromate-free chemical conversion
coating layer is preferably more than or equal to 0.1 mass % and
less than or equal to 10 mass % with respect to the total solid
content of the chemical conversion coating layer, and is more
preferably more than or equal to 1 mass % and less than or equal to
5 mass % with respect to the total solid content of the chemical
conversion coating layer.
[0056] Further, the chromate-free chemical conversion coating layer
of the steel sheet according to the present invention may further
contain a polyolefin lubricant. In such a case, slidability while
press working is performed on the steel sheet can be reduced. The
content of the polyolefin lubricant in the chromate-free chemical
conversion coating layer is preferably more than or equal to 0.1
mass % and less than or equal to 10 mass % with respect to the
total solid content of the chemical conversion coating layer, and
is more preferably more than or equal to 1 mass % and less than or
equal to 5 mass % with respect to the total solid content of the
chemical conversion coating layer.
[0057] The chromate-free chemical conversion coating layer of the
steel sheet according to the present invention may be an organic
coating layer or may also be an inorganic coating film layer.
However, in the case where higher corrosion resistance with respect
to deteriorated gasoline is demanded, it is desired that the
chromate-free chemical conversion coating layer do not contain an
organic resin component or contain an organic resin component the
amount of which is minimized. This is because it is estimated that
the organic resin component contained in the chromate-free chemical
conversion coating layer lowers the corrosion resistance since the
organic resin component is swelled by the fuel. Specific examples
of the organic resin component contained in the chromate-free
chemical conversion coating layer include an acrylic resin, an
olefin resin, a urethane resin, an epoxy resin, and a polyester
resin. The content of those organic resin components in the
chromate-free chemical conversion coating layer is preferably less
than or equal to 50 mass %, more preferably less than or equal to
30 mass %, and most preferably 0 mass % with respect to the total
solid content of the chemical conversion coating layer.
[0058] Moreover, the chromate-free chemical conversion coating
layer of the steel sheet according to the present invention may
contain, as an inorganic component, a silane coupling agent, a
condensation polymer of a silane coupling agent, silica, silicate,
phosphoric acid, and phosphate. The chromate-free chemical
conversion coating layer of the steel sheet according to the
present invention may be formed by containing one of those
components or two or more of those components in combination, or by
being mixed with the above-mentioned organic resin components. Note
that, the chromate-free chemical conversion coating layer may be
blended with other components including the above-mentioned
polyolefin lubricant, in a range that does not deteriorate the
characteristics.
[0059] Note that the chromate-free chemical conversion coating film
of the steel sheet according to the present invention can be formed
through a known method. For example, the method involves preparing
application liquid containing predetermined component(s) described
above, applying the prepared application liquid over the Zn plated
layer or the Zn--Ni alloy plated layer through a known method such
as bar coater and roll coater, and then heating at predetermined
heating temperature and drying the applied film.
[0060] As described above, in order to make the weldability of the
steel sheet satisfactory, or, in order to make the external
appearance of the coating of the surface to be the outer surface of
the fuel tank satisfactory, it is preferred that the surface to be
the outer surface of the fuel tank do not have the plated layer. In
order to make the outer surface into a state that does not have the
plated layer, there can be employed a method not involving applying
electric current to the side of the non-plated surface during
electroplating. Alternatively, there can be employed a method
involving performing plating, and then removing the plating on the
side of the non-plated surface through an electrochemical method
(for example, anode electrolytic treatment) or a mechanical method
(for example, grinding with a brush). Further, the above-mentioned
methods can be used in combination.
[0061] Owing to the above methods, the non-plated surface (outer
surface of the fuel tank) of the steel sheet according to the
present invention can be completely prevented from having Zn and/or
Ni being deposited thereon. In that case, the deposition amount of
Zn and/or Ni is 0. As described above, this is for improving the
weldability and the coating property of the steel sheet. It is
desirable that the deposition amount be 0.01 to 0.5 g/m.sup.2,
preferably 0.01 to 0.3 g/m.sup.2, more preferably 0.01 to 0.1
g/m.sup.2.
[0062] The contact angle on the non-plated surface (outer surface)
formed through those methods is preferably less than 10 degrees and
more preferably less than 5 degrees in the n-hexadecane contact
angle. In this way, the press workability and the coating property
are improved. In order to ensure the above contact angle, it is
effective to suppress oxidation on the surface of the steel sheet,
and in this point, it is desirable that a trace amount of Zn and/or
Ni is present also on the non-plated surface side. The deposition
amount is desirably 0.01 to 0.5 g/m.sup.2.
EXAMPLES
[0063] Next, the present invention will be described further
specifically with reference to Examples and Comparative
Examples.
[0064] First, using a non-plated steel sheet, one-surface plated
steel sheets, and both-surfaces plated steel sheets shown in Table
1 as original sheets, surface treated steel sheets for a fuel tank
were produced. Note that the steel sheets shown in Table 1 were
each a Ti-added extra-low carbon steel sheet for deep drawing
having a thickness of 0.8 mm, and each chemical conversion coating
layer was formed only on one surface (the surface to be the inner
surface of the fuel tank) of the original sheet or on both surfaces
of the original sheet. Note that the compositions of the base
coating films that constitute the respective chemical conversion
coating layers are shown in Table 2. Further, to the base coating
films shown in Table 2, polyolefin lubricants shown in Table 3 and
fluorine-based water-and-oil repellents shown in Table 4 were each
added in a proportion shown in Table 5, and the chemical conversion
coating layers were formed.
TABLE-US-00002 TABLE 1 Symbol Content S/S non-plated steel sheet
S/5 Zn--Ni alloy plating (coating weight: 5 g/m.sup.2, Ni: 12.5%)
on only one surface (surface to be inner surface) S/15 Zn--Ni alloy
plating (coating weight: 15 g/m.sup.2, Ni: 11%) on only one surface
(surface to be inner surface) S/20 Zn--Ni alloy plating (coating
weight: 20 g/m.sup.2, Ni: 10.5%) on only one surface (surface to be
inner surface) S/30 Zn--Ni alloy plating (coating weight: 30
g/m.sup.2, Ni: 10.6%) on only one surface (surface to be inner
surface) S/40 Zn--Ni alloy plating (coating weight: 40 g/m.sup.2,
Ni: 10.1%) on only one surface (surface to be inner surface) 20/20
Zn--Ni alloy plating (coating weight: 20 g/m.sup.2, Ni: 10.5%) on
both surfaces S/EG40 Zn plating (coating weight: 40 g/m.sup.2) on
only one surface (surface to be inner surface) EG Zn plated steel
sheet (coating weight: 30 g/m.sup.2) on both surfaces
TABLE-US-00003 TABLE 2 Composition of base coating film (solid
content, mass %) a b c d e f g h i Organic Urethane resin (*1) 75
-- -- -- -- -- 50 30 10 resin Ionomer resin (*2) -- 60 -- -- -- --
-- -- -- Other than Silica 20 30 -- 10 -- 20 -- -- -- organic
Silane coupling agent (*3) 2 8 -- 9 -- 2 -- -- -- resin Silane
coupling agent oligomer (*4) -- -- 89 -- -- -- 44.5 62.3 80.1
Lithium silicate -- -- -- 75 -- -- -- -- -- Phosphoric acid -- -- 5
-- -- -- 2.5 3.5 4.5 Aluminum primary phosphate -- -- -- -- 55 --
-- -- -- Magnesium primary phosphate -- -- -- -- -- 40 -- -- --
Ammonium phosphate 1 2 -- 1 -- -- -- -- -- Phosphoric acid (*5) --
-- -- -- 30 30 -- -- -- Vanadyl acetylacetonate 2 -- 3 2 -- -- 1.5
2.1 2.7 Ammonium vanadate -- -- -- -- 5 4 -- -- -- Ammonium
hexafluorotitanate -- -- 1 1 5 4 0.5 0.7 0.9 Tetra-n-butoxy
titanate -- -- -- -- 5 -- -- -- -- Zirconium oxycarbonate -- -- 2 2
-- -- 1 1.4 1.8 Total 100 100 100 100 100 100 100 100 100
[0065] Note that, in Table 2, "urethane resin (*1)" represents an
ester-based urethane resin, "ionomer resin (*2)" represents a Na
neutralized ionomer resin, "silane coupling agent (*3)" represents
3-glycidoxypropyl trimethoxy silane, "silane coupling agent
oligomer (*4)" represents a condensation polymer of
3-glycidoxypropyl trimethoxy silane and
3-aminopropyltriethoxysilane in a ratio of 1:1 (molecular weight of
approximately 3000), and "phosphonic acid (*5)" represents
1-hydroxy-ethylidene-1,1'-diphosphonic acid. Further, "-" in Table
2 shows that no corresponding component is blended.
TABLE-US-00004 TABLE 3 Symbol Content PE Polyethylene wax PP
Polypropylene wax
TABLE-US-00005 TABLE 4 Symbol Content F1 Polytetrafluoroethylene F2
Tetrafluoroethylene - hexafluoropropylene copolymer F3
Tetrafluoroethylene - perfluoroalkyl vinyl ether copolymer F4
Perfluoroalkyl vinyl ether - methacrylate copolymer
TABLE-US-00006 TABLE 5 Mass ratio (solid content) with respect to
solid content 100 of base coating film Base Polyolefin
Fluorine-based Coating coating lubricant water-and-oil repellent
film No. film PE PP F1 F2 F3 F4 A1 a 1 -- -- -- -- -- A2 a 5 -- --
-- -- -- A3 a 10 -- -- -- -- -- A4 a -- 5 -- -- -- 5 B1 b 5 -- --
-- -- -- B2 b -- -- -- -- -- 5 B3 b 5 -- 5 -- -- -- B4 b 5 -- 5 --
-- 3 C1 c 5 -- -- -- -- -- C2 c -- -- -- -- -- 0.1 C3 c -- -- -- --
-- 0.5 C4 c -- -- -- -- -- 1 C5 c -- -- -- -- -- 5 C6 c -- -- -- --
-- 10 C7 c -- -- 5 -- -- 10 C8 c 3 -- -- -- -- 5 D1 d -- -- 2 -- --
-- D2 d -- -- -- 3 -- -- D3 d -- -- -- -- 3 -- E1 e -- -- -- -- --
3 E2 e -- 2 -- -- -- 3 E3 e 2 -- -- -- -- 3 F1 f -- -- -- 3 -- --
F2 f -- -- -- -- 3 -- G1 g -- -- -- -- -- 5 H1 h -- -- -- -- -- 5
I1 I -- -- -- -- -- 5
[0066] Note that "-" in Table 5 shows that no corresponding
component is blended.
[0067] Subsequently, Tables 6 to 8 each show sample preparation
conditions, and performance evaluation results of the prepared
steel sheets. Here, the contact angle of the surface to be the
inner surface of the fuel tank was measured as follows.
(Water Contact Angle)
[0068] A contact angle meter (DM-901 manufactured by Kyowa
Interface Science Co., Ltd) was used, 3 .mu.l of ion exchanged
water were dripped under 25.degree. C. atmosphere, and a static
contact angle after 60 seconds was measured.
(n-hexadecane Contact Angle)
[0069] A contact angle meter (DM-901 manufactured by Kyowa
Interface Science Co., Ltd) was used, 3 .mu.l of n-hexadecane were
dripped under 25.degree. C. atmosphere, and a static contact angle
after 60 seconds was measured.
[0070] Performance evaluation was carried out as follows.
(Primary Rust Resistance)
[0071] To the prepared sample, rust-resistant oil (NOX-RUST 530,
manufactured by Parker Industries, Inc.) was applied extremely
slightly (approximately 0.1 g/m.sup.2), and then the resultant was
packed in a manner that the surface to be the inner surface and the
surface to be the outer surface came into contact with each other
so that the state looked like a coil. After stored in 50.degree. C.
98%RH environment for one month, the resultant was unpacked, and a
rust state on the surface to be an outer surface of a fuel tank was
observed. Note that the observation results were evaluated using
the following criteria.
[0072] Satisfactory: no rust or discoloration
[0073] Unsatisfactory: occurrence of white rust or
discoloration
[0074] Poor: occurrence of red rust
(Coating Property)
[0075] The coating property of the surface to be the outer surface
was evaluated. Since the outer surface of the fuel tank for an
automobile or a motorcycle is normally coated after being subjected
to chemical conversion treatment for pre-coating treatment, the
external appearance of the coating is dominated by an external
appearance after being subjected to the chemical conversion
treatment for pre-coating treatment. Accordingly, a steel sheet
after being subjected to the chemical conversion treatment for
pre-coating treatment was evaluated for the external appearance of
the surface to be the outer surface. Note that the chemical
conversion treatment for pre-coating treatment was carried out as
follows.
[0076] A chemical conversion coating layer was formed through
P-free chemical conversion treatment (Example 1 in JP 5274560B)
consisting of hexafluorozirconic acid, aluminum nitrate, and
polyethyleneimine. After that, the steel sheet over which the
chemical conversion coating layer had been formed was evaluated by
visual observation (however, in the case where it was difficult to
perform evaluation by visual observation, the observation was
performed using a scanning electron microscope (SEM)), and the
evaluation was performed using the following criteria.
[0077] Excellent: uniform external appearance
[0078] Satisfactory: slight unevenness of an acceptable level
[0079] Unsatisfactory: remarkable unevenness
[0080] Poor: occurrence of lack of hiding (no chemical conversion
coating layer)
(Coating Property After Storage)
[0081] A sample stored for one month was used in the same manner as
the above-mentioned evaluation of primary rust resistance, the same
chemical conversion treatment for pre-coating treatment as the
above-mentioned evaluation of coating property was performed, and
the evaluation was performed using the same criteria.
(Workability (Slidability))
[0082] Evaluation was performed by a draw bead test. Using a die
having a convex bead end of 5R and a concave shoulder of 3R, a
sample (to which rust-resistant oil (NOX-RUST 530, manufactured by
Parker Industries, Inc.) was applied) which was cut to a width of
30 mm was drawn out 100 mm at a rate of 200 mm/min in a range of
500 kg to 1200 kg in terms of press bonding load. After that, a
coefficient of friction was determined using the relationship
between the press bonding load and a drawing load. Note that the
surface to be the inner surface of the fuel tank was set on the
convex bead side. Further, no oil was applied to the bead die, and
the test was performed by wiping off the oil on the die for every
test. The coefficient of friction was evaluated using the following
criteria.
[0083] Excellent: coefficient of friction.ltoreq.0.13
[0084] Satisfactory: 0.13<coefficient of
friction.ltoreq.0.15
[0085] Unsatisfactory: 0.15<coefficient of friction<0.2
[0086] Poor: 0.2.ltoreq.coefficient of friction
(Deteriorated Gasoline-Corrosion Resistance)
[0087] A steel sheet was molded in a cylinder shape having an
inside diameter of 50 mm and a depth of 35 mm, which imitates a
fuel tank. After removing oil through grease removing treatment, a
flaw that reaches up to the base metal was made by a cutter on the
inner surface base (which imitates a flaw caused by press working).
After that, test liquid that imitates the deteriorated gasoline
(gasoline containing 100 ppm of formic acid, 300 ppm of acetic
acid, 100 ppm of chloride ions, 1.0 vol % of water) was enclosed in
the molded steel sheet, and was retained at 40.degree. C. for two
months. After that, the corrosion state of the steel sheet was
evaluated using the following criteria.
[0088] Excellent: no corrosion
[0089] Satisfactory: slight rust (at a level that no thickness
reduction occurred due to corrosion)
[0090] Unsatisfactory: partially corroded
[0091] Poor: corrosion over entire surface
TABLE-US-00007 TABLE 6 Amount of Performance Coating film coating
Contact angle Primary Coating Original Coating formed film on inner
surface rust Coating property after Work- Corrosion sheet film No
surface [g/m.sup.2] Water n-hexadecane resistance property storage
ability resistance Example 1 S/20 A4 Inner surface 0.6 90 69
Satisfactory Excellent Excellent Excellent Satisfactory only
Example 2 S/20 B2 Inner surface 0.6 99 70 Satisfactory Excellent
Excellent Satis- Satisfactory only factory Example 3 S/20 C3 Inner
surface 0.6 70 30 Satisfactory Excellent Excellent Satis-
Satisfactory only factory Example 4 S/20 C4 Inner surface 0.6 90 60
Satisfactory Excellent Excellent Satis- Excellent only factory
Example 5 S/20 C5 Inner surface 0.6 95 65 Satisfactory Excellent
Excellent Satis- Excellent only factory Example 6 S/20 C6 Inner
surface 0.6 99 69 Satisfactory Excellent Excellent Satis- Excellent
only factory Example 7 S/20 C7 Inner surface 0.6 105 70
Satisfactory Excellent Excellent Satis- Excellent only factory
Example 8 S/20 C8 Inner surface 0.6 91 67 Satisfactory Excellent
Excellent Excellent Excellent only Example 9 S/20 D1 Inner surface
0.6 85 55 Satisfactory Excellent Excellent Satis- Excellent only
factory Example 10 S/20 D2 Inner surface 0.6 85 62 Satisfactory
Excellent Excellent Satis- Excellent only factory Example 11 S/20
D3 Inner surface 0.6 87 63 Satisfactory Excellent Excellent Satis-
Excellent only factory Example 12 S/20 E1 Inner surface 0.6 89 64
Satisfactory Facallent Excellent Satis- Excellent only factory
Example 13 S/20 E2 Inner surface 0.6 92 65 Satisfactory Excellent
Excellent Excellent Excellent only Example 14 S/20 E3 Inner surface
0.6 91 65 Satisfactory Excellent Excellent Excellent Excellent only
Example 15 S/20 F1 Inner surface 0.6 89 63 Satisfactory Excellent
Excellent Satis- Excellent only factory Example 16 S/20 F2 Inner
surface 0.6 90 64 Satisfactory Excellent Excellent Satis- Excellent
only factory Example 17 S/20 G1 Inner surface 0.6 95 67
Satisfactory Excellent Excellent Satis- Satisfactory only factory
Example 18 S/20 H1 Inner surface 0.6 93 66 Satisfactory Excellent
Excellent Satis- Satisfactory only factory Example 19 S/20 I1 Inner
surface 0.6 92 66 Satisfactory Excellent Excellent Satis-
Satisfactory only factory Example 20 20/20 A4 Inner surface 0.4 90
69 Satisfactory Excellent Satisfactory Excellent Satisfactory only
Example 21 20/20 B2 Inner surface 0.4 99 70 Satisfactory Excellent
Satisfactory Satis- Satisfactory only factory Example 22 20/20 C3
Inner surface 0.4 70 30 Satisfactory Excellent Satisfactory Satis-
Satisfactory only factory Example 23 20/20 C4 Inner surface 0.4 90
60 Satisfactory Excellent Satisfactory Satis- Excellent only
factory Example 24 20/20 C5 Inner surface 0.4 95 65 Satisfactory
Excellent Satisfactory Satis- Excellent only factory Example 25
20/20 C6 Inner surface 0.4 99 69 Satisfactory Excellent
Satisfactory Satis- Excellent only factory Example 26 20/20 C7
Inner surface 0.4 105 70 Satisfactory Excellent Satisfactory Satis-
Excellent only factory Example 27 20/20 C8 Inner surface 0.4 91 67
Satisfactory Excellent Satisfactory Excellent Excellent only
Example 28 20/20 D1 Inner surface 0.4 85 55 Satisfactory Excellent
Satisfactory Satis- Excellent only factory Example 29 20/20 D2
Inner surface 0.4 85 62 Satisfactory Excellent Satisfactory Satis-
Excellent only factory Example 30 20/20 D3 Inner surface 0.4 87 63
Satisfactory Excellent Satisfactory Satis- Excellent only factory
Example 31 20/20 E1 Inner surface 0.4 89 64 Satisfactory Excellent
Satisfactory Satis- Excellent only factory Example 32 20/20 E2
Inner surface 0.4 92 65 Satisfactory Excellent Satisfactory
Excellent Excellent only Example 33 20/20 E3 Inner surface 0.4 91
65 Satisfactory Excellent Satisfactory Excellent Excellent only
TABLE-US-00008 TABLE 7 Performance Coating film Amount of Contact
angle Primary Coating Original Coating formed coating film on inner
surface rust Coating property after Work- Corrosion sheet film No
surface [g/m.sup.2] Water n-hexadecane resistance property storage
ability resistance Example 34 20/20 F1 Inner surface 0.4 89 63
Satis- Excellent Satisfactory Satis- Excellent only factory factory
Example 35 20/20 F2 Inner surface 0.4 90 64 Satis- Excellent
Satisfactory Satis- Excellent only factory factory Example 36 20/20
G1 Inner surface 0.4 95 67 Satis- Excellent Satisfactory Satis-
Satis- only factory factory factory Example 37 20/20 H1 Inner
surface 0.4 93 66 Satis- Excellent Satisfactory Satis- Satis- only
factory factory factory Example 38 20/20 I1 Inner surface 0.4 92 66
Satis- Excellent Satisfactory Satis- Satis- only factory factory
factory Example 39 S/5 C5 Inner surface 0.6 95 65 Satis- Excellent
Excellent Satis- Satis- only factory factory factory Example 40 S/5
D2 Inner surface 0.6 85 62 Satis- Excellent Excellent Satis- Satis-
only factory factory factory Example 41 S/5 E1 Inner surface 0.6 89
64 Satis- Excellent Excellent Satis- Satis- only factory factory
factory Example 42 S/5 F1 Inner surface 0.6 89 63 Satis- Excellent
Excellent Satis- Satis- only factory factory factory Example 43
S/15 C5 Inner surface 0.6 95 65 Satis- Excellent Excellent Satis-
Excellent only factory factory Example 44 S/15 D2 Inner surface 0.6
85 62 Satis- Excellent Excellent Satis- Excellent only factory
factory Example 45 S/15 E1 Inner surface 0.6 89 64 Satis- Excellent
Excellent Satis- Excellent only factory factory Example 46 S/15 F1
Inner surface 0.6 89 63 Satis- Excellent Excellent Satis- Excellent
only factory factory Example 47 S/30 C5 Inner surface 0.6 95 65
Satis- Excellent Excellent Satis- Excellent only factory factory
Example 48 S/30 D2 Inner surface 0.6 85 62 Satis- Excellent
Excellent Satis- Excellent only factory factory Example 49 S/30 E1
Inner surface 0.6 89 64 Satis- Excellent Excellent Satis- Excellent
only factory factory Example 50 S/30 F1 Inner surface 0.6 89 63
Satis- Excellent Excellent Satis- Excellent only factory factory
Example 51 S/40 C5 Inner surface 0.6 95 65 Satis- Excellent
Excellent Satis- Excellent only factory factory Example 52 S/40 D2
Inner surface 0.6 85 62 Satis- Excellent Excellent Satis- Excellent
only factory factory Example 53 S/40 E1 Inner surface 0.6 89 64
Satis- Excellent Excellent Satis- Excellent only factory factory
Example 54 S/40 F1 Inner surface 0.6 89 63 Satis- Excellent
Excellent Satis- Excellent only factory factory Example 55 S/20 C5
Inner surface 0.1 90 61 Satis- Excellent Excellent Satis- Satis-
only factory factory factory Example 56 S/20 C5 Inner surface 0.3
95 65 Satis- Excellent Excellent Satis- Excellent only factory
factory Example 57 S/20 C5 Inner surface 0.8 95 65 Satis- Excellent
Excellent Satis- Excellent only factory factory Example 58 S/20 C5
Inner surface 1.2 95 65 Satis- Excellent Excellent Satis- Excellent
only factory factory Example 59 S/20 C5 Inner surface 1.5 95 65
Satis- Excellent Excellent Satis- Excellent only factory factory
Example 60 S/20 C5 Inner surface 2 95 65 Satis- Excellent Excellent
Satis- Excellent only factory factory Example 61 S/20 D2 tuner
surface 0.3 85 62 Satis- Excellent Excellent Satis- Excellent only
factory factory Example 62 S/20 D2 Inner surface 1.2 85 62 Satis-
Excellent Excellent Satis- Excellent only factory factory Example
63 S/20 E1 Irmer surface 0.3 89 64 Satis- Excellent Excellent
Satis- Excellent only factory factory Example 64 S/20 E1 Inner
surface 1.2 89 64 Satis- Excellent Excellent Satis- Excellent only
factory factory Example 65 S/20 F1 Inner surface 0.3 89 63 Satis-
Excellent Excellent Satis- Excellent only factory factory Example
66 S/20 F1 Inner surface 1.2 89 63 Satis- Excellent Excellent
Satis- Excellent only factory factory Example 67 S/EG40 F1 Inner
surface 0.3 89 63 Satis- Excellent Excellent Satis- Satis- only
factory factory factory Example 68 S/EG40 F1 Inner surface 1.2 89
63 Satis- Excellent Excellent Satis- Satis- only factory factory
factory
TABLE-US-00009 TABLE 8 Amount Performance Coat- Coating of Contact
angle Coating ing film coating on inner surface Primary property
Original film formed film n- rust Coating after Work- Corrosion
sheet No surface [g/m.sup.2] Water hexadecane resistance property
storage ability resistance Comparative S/20 A1 Inner surface 0.6 50
10 Satisfactory Excellent Excellent Excellent Poor Example 1 only
Comparative S/20 A2 Inner surface 0.6 65 12 Satisfactory Excellent
Excellent Excellent Unsatis- Example 2 only factory Comparative
S/20 A3 Inner surface 0.6 70 15 Satisfactory Excellent Excellent
Excellent Unsatis- Example 3 only factory Comparative S/20 B1 Inner
surface 0.6 75 25 Satisfactory Excellent Excellent Excellent
Unsatis- Example 4 only factory Comparative S/20 B3 Inner surface
0.6 108 75 Poor Excellent Poor Unsatis- Satisfactory Example 5 only
factory Comparative S/20 B4 Inner surface 0.6 115 80 Poor Excellent
Poor Poor Unsatis- Example 6 only factory Comparative S/20 C1 Inner
surface 0.6 50 0 Satisfactory Excellent Excellent Excellent Poor
Example 7 only Comparative S/20 C2 Inner surface 0.6 40 25
Satisfactory Excellent Excellent Satisfactory Poor Example 8 only
Comparative 20/20 A1 Inner surface 0.4 50 10 Satisfactory Excellent
Excellent Excellent Poor Example 9 only Comparative 20/20 A2 Inner
surface 0.4 65 12 Satisfactory Excellent Excellent Excellent
Unsatis- Example 10 only factory Comparative 20/20 A3 Inner surface
0.4 70 15 Satisfactory Excellent Excellent Excellent Unsatis-
Example 11 only factory Comparative 20/20 B1 Inner surface 0.4 75
25 Satisfactory Excellent Excellent Excellent Unsatis- Example 12
only factory Comparative 20/20 B3 Inner surface 0.4 108 75 Unsatis-
Excellent Poor Poor Satisfactory Example 13 only factory
Comparative 20/20 B4 Inner surface 0.4 115 80 Unsatis- Excellent
Poor Poor Unsatis- Example 14 only factory factory Comparative
20/20 C1 Inner surface 0.4 50 0 Satisfactory Excellent Excellent
Excellent Poor Example 15 only Comparative 20/20 C2 Inner surface
0.4 40 25 Satisfactory Excellent Excellent Satisfactory Poor
Example 16 only Comparative 20/20 A1 Both surfaces 0.6 50 10
Satisfactory Poor Poor Excellent Poor Example 17 Comparative 20/20
B2 Both surfaces 0.6 99 70 Satisfactory Poor Poor Poor Poor Example
18 Comparative 20/20 B3 Both surfaces 0.6 108 75 Satisfactory Poor
Poor Poor Poor Example 19 Comparative 20/20 C2 Both surfaces 0.6 40
25 Satisfactory Poor Poor Satisfactory Poor Example 20 Comparative
20/20 C3 Both surfaces 0.6 70 30 Satisfactory Poor Poor Unsatis-
Unsatis- Example 21 factory factory Comparative 20/20 C4 Both
surfaces 0.6 90 60 Satisfactory Poor Poor Poor Unsatis- Example 22
factory Comparative S/S C5 Inner surface 1 93 63 Satisfactory
Excellent Excellent Satisfactory Poor Example 23 only Comparative
EG C5 Inner surface 0.6 94 64 Satisfactory Excellent Unsatis- Poor
Poor Example 24 only factory
[0092] As shown in the results in Tables 6 to 8, Examples according
to the present invention showed evaluations of "Satisfactory" or
higher in every evaluation item, and had satisfactory
characteristics. To be specific, regarding the primary rust
resistance, rust occurred in Comparative Examples 5, 6, 13, and 14
in which the n-hexadecane contact angles exceeded the upper limit
of the present invention. Further, regarding the coating property,
Examples and Comparative Examples other than Comparative Examples
17 to 22, each of which had the chemical conversion coating layer
formed on the surface to be the outer surface, showed satisfactory
evaluations of "Excellent", however, regarding the coating property
after storage, evaluation results remarkably deteriorated in each
of Comparative Examples 5, 6, 13, and 14 in which rust occurred in
the primary rust. In addition, as shown in Table 9, regarding the
coating property after storage, slight unevenness of an acceptable
level occurred in each of Examples 20 to 38 in which the Zn--Ni
alloy plated layer was also provided on the surface to be the outer
surface. Therefore, it was found that it is more preferred that the
steel sheet according to the present invention have a non-plated
outer surface. Note that, although each of Comparative Examples 9
to 12, 15, and 16 had the Zn--Ni alloy plated layer on the surface
to be the outer surface, the coating property after storage was
"Excellent", since the n-hexadecane contact angle on the inner
surface was less than the lower limit according to the present
invention. However, because the n-hexadecane contact angle on the
inner surface was less than the lower limit according to the
present invention, the corrosion resistance deteriorated. Regarding
the workability (slidability), the workability remarkably
deteriorated in each of Comparative Examples 5, 6, 13, and 14 in
which the n-hexadecane contact angle exceeded the upper limit of
the present invention and in each of Comparative Examples 18, 19,
21, and 22 in which, although the n-hexadecane contact angle was
within the range of the present invention, the chemical conversion
coating layers were formed on both inner and outer surfaces.
Moreover, comparing Examples according to the present invention
with each other, evaluations were more satisfactory in each of
Examples 1, 8, 13, 14, 20, 27, 32, and 33 to which polyolefin wax
was added. Regarding the corrosion resistance with respect to
deteriorated gasoline, Examples according to the present invention
showed satisfactory evaluations, and in particular, Examples 3 to
16, 22 to 35, and 43 to 66, each of which used, as the
chromate-free chemical conversion coating layer, an inorganic
coating film not containing an organic resin component other than
polyolefin wax and a fluorine-based resin, showed more preferable
evaluations. Further, it was found that Examples 4 to 16, 23 to 35,
and 43 to 66, each of which had the n-hexadecane contact angle of
more than or equal to 55 degrees, showed more preferable
evaluations. Still further, referring to Examples 55 to 60, in the
case where the deposition amount of the chemical conversion coating
layer was more than or equal to 0.3 g/m.sup.2, it was found that
the corrosion resistance was more preferable. In addition,
referring to Examples 39 to 42, in the case where the deposition
amount of the Zn--Ni alloy plated layer per surface is more than or
equal to 15 g/m.sup.2, it was found that the corrosion resistance
was more preferable.
TABLE-US-00010 TABLE 9 Amount Contact Performance Coat- of
Deposition angle Coating Appro- ing Coating film coating amount on
outer on outer property priate Original film formed film surface
[g/m.sup.2] surface Coating after welding sheet No surface
[g/m.sup.2] Zn Ni n-hexadecane property storage range Example 5
S/20 C5 Inner surface 0.6 0.05 0.1 Less than 5 Excellent Excellent
3.7 kA only Example 24 20/20 C5 Inner surface 0.4 17.9 2.1 Less
than 5 Excellent Satis- 3.0 kA only factory Example 58 S/20 C5
Inner surface 1.2 0.05 0.1 Less than 5 Excellent Excellent 3.6 kA
only Example 59 S/20 C5 Inner surface 1.5 0.05 0.1 Less than 5
Excellent Excellent 3.0 kA only Example 67 S/EG40 F1 Inner surface
0.3 0.2 0 Less than 5 Excellent Excellent 3.0 kA only Example 69
S/20*1 C5 Inner surface 0.6 0.0 0.0 10 Satis- Satis- 3.7 kA only
factory factory Example 70 S/20*2 C5 Inner surface 0.6 1.05 0.1
Less than 5 Satis- Satis- 3.5 kA only factory factory Example 71 S/
F1 Inner surface 0.3 0 0 10 Satis- Satis- 3.0 kA EG40*1 only
factory factory Example 72 S/ F1 Inner surface 0.3 1.2 0 Less than
5 Satis- Satis- 3.0 kA EG40*2 only factory factory Example 73 S/ C5
Inner surface 0.3 0 0.01 Less than 5 Excellent Excellent 3.7 kA
EG40*2 only Example 74 S/ F1 Inner surface 0.3 1.0 0 Less than 5
Satis- Satis- 3.7 kA EG40*2 only factory factory Example 75 S/ F1
Inner surface 0.3 0.3 0 Less than 5 Excellent Excellent 3.7 kA
EG40*2 only Example 76 S/ F1 Inner surface 0.3 0.0 0.1 Less than 5
Excellent Excellent 3.7 kA EG40*2 only Example 77 S/ F1 Inner
surface 0.3 0.0 0.5 Less than 5 Excellent Excellent 3.7 kA EG40*2
only Comparative 20/20 C4 Both surfaces 0.6 17.9 2.1 60 Poor Poor
2.5 kA Example 22 *1A slight amount of deposition on the outer
surface was completely removed. *2Zn or Ni was additionally plated
on the outer surface.
[0093] For the one-surface-plated materials of the original sheets
shown in Table 1, the non-plated surface sides were each analyzed
in detail, and approximately 0.1 g/m.sup.2 of Zn and Ni was
detected. In the results shown in Table 9, for confirming a slight
amount of Zn and Ni on the non-plated surface side, the original
sheets of S/20 and S/EG40 shown in Table 1 were used, each of the
plated surface sides was sealed with a tape, then each of the
non-plated surface sides was polished using abrasive paper of #800,
and after that, anode electrolytic treatment was performed to
completely remove the slight amount of Zn and Ni (*1: Examples 69
and 71). Alternatively, S/20 and S/EG40 were used, each of the
plated surface sides was sealed with a tape, and then
electroplating of a predetermined amount of Zn or Ni was performed
on each of the non-plated surface sides (*2: Examples 70, 72, and
74 to 77). After that, in the same manner as the preceding
examples, predetermined coating treatment was performed to prepare
samples of Examples 69 to 77. Those samples and, among the samples
shown in Tables 6 to 8, Example 5, Example 24, Example 58, Example
59, and Comparative Example 22 were selected, and measurement of
the contact angles on the outer surfaces, evaluation of the coating
properties, and evaluation of the coating properties after storage
were performed. The method of evaluating those samples and the
criteria for the evaluations are the same as those shown above.
[0094] For those samples, seam weldability evaluation was
performed. The surfaces to be the inner surfaces were placed
together. The seam welding conditions are as follows. [0095]
Electrode: a disc-shaped electrode made of a Cu--Cr alloy, in which
a cross section at a central part had a radius of 15 mm and a width
of 4.5 mm and a cross section at an end part had a radius of 4 mm
and a width of 8 mm [0096] Welding method: piling of two sheets,
lap seam welding [0097] Welding pressure: 400 kgf (note that 1 kgf
is approximately 9.8 N) [0098] Welding time: 2/50 sec on, 1/50 sec
off [0099] Cooling: inner part water cooled, and outer part water
cooled [0100] Welding speed: 2.5 m/min
[0101] A range of current in which an appropriate nugget can be
obtained was determined by changing the welding current.
[0102] Table 10 shows the results. In the lap seam welding, it is
considered to be practically acceptable as long as the appropriate
current range is more than or equal to approximately 3 kA, and it
is preferred that the range be wider. Accordingly, comparing
Examples 5 and 24 with each other, it was found that one-surface
plating was more preferable than the both-surfaces plating.
Further, comparing Examples 5, 58, and 59 with each other, it was
found that the upper limit of the coating amount of the chemical
conversion coating layer was preferably approximately 1.2
g/m.sup.2.
TABLE-US-00011 TABLE 10 Appropriate welding range Example 5 More
than or equal to 3.7 kA Example 24 More than or equal to 3.0 kA
Example 58 More than or equal to 3.6 kA Example 59 More than or
equal to 3.0 kA Comparative Example 22 More than or equal to 2.5
kA
[0103] The preferred examples of the present invention have been
described above, whilst the present invention is not limited to the
above examples. A person skilled in the art may find various
alterations and modifications within the scope of the appended
claims, and it should be understood that they will naturally come
under the technical scope of the present invention.
INDUSTRIAL APPLICABILITY
[0104] The present invention is industrially useful, because the
present invention can provide the surface treated steel sheet for a
fuel tank, which exhibits excellent corrosion resistance under an
environment in which various fuels are enclosed, the fuels
including a fuel containing an organic acid such as deteriorated
gasoline and a fuel containing dew condensation water in addition
to an organic acid, and which has satisfactory press
workability.
[0105] Moreover, the present invention provides the steel sheet
having different surface states between the inner and outer
surfaces, by making the surface to be the outer surface of the fuel
tank to be base metal and making the surface to be the inner
surface of the fuel tank to be the chromate-free chemical
conversion coating film. Such a steel sheet according to the
present invention has every performance necessary from the
production of the fuel tank to the using of the fuel tank: (i)
excellent workability that is necessary during processing and
welding of the steel sheet to make the steel sheet into a tank
shape; (ii) excellent coating property that is necessary during
coating of the processed tank to enhance the visual quality of the
external appearance; and (iii) excellent corrosion resistance that
is necessary for using the produced tank for a long time. The steel
sheet according to the present invention also has an effect that is
not conventionally achieved in the point that the surface states
that are different between the inner and outer surfaces interact
with each other and differences in performances between the inner
and outer surfaces can be further exhibited.
* * * * *